1. Field of the Invention
This invention relates generally to electric motor control circuits and electric throttle sensor circuits. This invention relates more specifically to the control of a direct current electric motor whose speed is determined by the position of a manually operated throttle, wherein less than full discharge of a direct current power source through the motor is required. Most frequently this invention will find application in controlling of electric motors associated with battery powered vehicles.
2. Description of the Related Art
Efforts to get away from fossil fuel propelled engines and motors have lead to increased usage of electrically propelled engines and motors, especially as they might apply in manned or unmanned vehicles. One of the most significant problems associated with the widespread use of such electrical vehicles and devices is the necessity of maintaining an ample direct current electric power supply in direct association with the electric motor. New battery technologies have reduced the size and weight of direct current power storage devices, but have not altogether addressed the problems of frequent charging and recharging of the batteries for continued use. Efficient use of the stored power in such vehicles is therefore of great concern.
While efficiency in the use of fossil fuel driven engines is primarily a matter of capturing as much of the combustion energy output as possible, efficiency in the use of electrically driven motors primarily concerns regulating the power drain from a direct current power source in a manner that utilizes only such power as is required by the engine for the speed selected in the particular vehicle or application.
In the past, electric motor controller circuits have been designed to tap the direct current power source for a maximum flow of current based upon the highest expected electric motor speed that might be required and to simply channel a portion of the current off through some other current drain when the electric drive motor does not require such high levels of current. In most cases this channeling off of the excess, unneeded current or voltage potential resulted in the waste of such power and a resultant decrease in the efficient use of the power source. More often than not, this method of regulating current flow to the electric motor had a direct effect on the frequency of recharge for the direct current power source.
These earlier types of electric motor controllers typically utilized groups of resistive circuits to provide alternate current drains on the battery or direct current power source. These resistive circuits could be placed in parallel or in series with the electric motor and switched in and out depending upon the current requirements of the motor. It is well known, however, that such resistive circuits continue to drain significant current from a battery and to dissipate such energy in the form of heat. Such approaches, therefore, do not do much for the efficiency of the motor or the vehicle it propels.
Efforts have been made in the past to regulate current flow from a direct current power source through an electric motor in a manner that does not simply channel the current into another current drain. Such efforts have focused on the use of solid state switching devices to pulse the current through an electric motor in a manner that effectively opens and closes a circuit between the direct current power source and the direct current drain (the electric motor) at a specific frequency and with pulse durations related to the desired speed of the motor. The greater the speed, the longer the duration of the current pulses in which the current flow through the motor is in a full on condition. The lower the desired speed, the longer the current pulses in which the flow of current is in an off condition. The current through the motor is always either in a full on condition or a full off condition with the ratio of on duration to off duration determining motor speed. Use of such solid state devices as silicone control rectifiers (SCRs) and metal oxide semiconductor field effect transistors (MOSFETs) have shown great promise in these applications.
Such circuits that utilize SCR and MOSFET devices, however, are only as efficient as their ability to translate some throttle indication of a desired motor speed to an appropriate current flow. This efficiency includes the ability to instill circuit reliability and overall motor and vehicle safety while achieving a longer recharge cycle. Past attempts to utilize such solid state circuit devices as SCRs and MOSFETs have not only suffered from reliability and ruggedness problems, but have also suffered from a complexity and expense not merited by the motors and devices that are intended to be controlled by the circuits. In other words, past attempts to accomplish the regulated control of current through a DC electric motor have succeeded, but only at the expense of unusual complexity and the associated lack of reliability and versatility that often accompanies such complexities.
Solid state current switching devices in applications of concern here, are typically controlled (gated) by a square wave signal having variant pulse widths. This gating square wave is typically generated by a pulse width modulator that translates a given voltage level into a related pulse width in the square wave signal. The voltage level itself, and therefore the pulse width of the square wave, is designed to be representative of a throttle or controller position for the motor or motor driven vehicle.
While basic pulse width modulation technology, as is briefly described above, may be well known in the field of controlling DC electric motors, very little has been done to instill this technology with circuit designs that provide the efficiency, features, functions, and characteristics desired by industries that utilize such DC motors. Many of these desired features and functions of such circuits have been identified in the industry, and to some extent have been addressed, but primarily only in association with other types of engines and propulsion systems. Means for controlling vehicle direction, modifying vehicle speed when direction changes, terminating motion of a vehicle under certain adverse safety conditions, and generally making the controller/propulsion system better able to withstand motion and temperature extremes, have all been addressed in association with internal combustion engines and the like. Unfortunately, the systems addressing these functions that are utilized in internal combustion engines do not translate easily into similar systems that utilize DC electric motors for propulsion. Because of the fundamental differences between internal combustion engines and electric motors, very few of the controller systems associated with the former can be implemented with the latter.
It would therefore be advantageous to have a motor/vehicle controller/throttle circuit that achieves not only the efficient operation of a DC electric motor, but additionally accomplishes the ancillary functions associated with such motors and vehicles and provides a reliable and rugged device that can implement safety features well known in the field of use for a particular vehicle or motor.